Systems and methods for communicating among network distribution points

ABSTRACT

A communication system has a trunk extending from a network facility, such as a central office, with a plurality of distribution points positioned along the trunk. Each leg of the trunk defines a shared channel that permits peak data rates much greater than what would be achievable without channel sharing. As an example, the connections of each respective trunk leg may be bonded. Further, the same modulation format and crosstalk vectoring are used for each leg of the trunk. The crosstalk vectoring cancels both far-end crosstalk (FEXT) that couples between connections of a given trunk leg and crossover crosstalk that couples between one trunk leg and another. In addition, logic determines an amount of excess capacity available for each leg of the trunk and controls error correction based on the determined excess capacity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S. Pat.No. 9,143,195, entitled “Systems and Methods for Communicating amongNetwork Distribution Points” and issued on Sep. 22, 2015, which isincorporated herein by reference.

RELATED ART

Telecommunication services have historically been delivered over the“last mile” (between a local exchange and the customer premises) overcopper cable facilities. To support high-speed data services over thesefacilities, service providers employ digital communication links, suchas Asymmetric Digital Subscriber Line (ADSL) or other similartechnologies over these copper facilities. A characteristic of DSL andthe copper channel is that the achievable data rate decreases as thelength of the copper pair increases. Therefore, to offer higher datarates, service providers have shortened the effective length of thecopper pair by moving the service provider transceiver of the DSL linkfrom the exchange to an intermediate point in the cable and using ashared fiber-optic facility to transport the signals between theexchange and the intermediate point (or node).

Despite increases in data rates enabled by shortening the length of thecopper facilities, the peak data rates for DSL services typically fallbelow those offered by Data Over Cable Service Interface Specification(DOCSIS) services. In this regard, a DOCSIS system uses coaxial cable,which permits a much higher peak data rate for a given subscriber thanthat available via conventional DSL over copper facilities. However, thecoaxial cable is shared among many customers such that the actual datarate provided to a particular customer, depending on the number ofcustomers actively communicating via the DOCSIS system, is often muchless and, at times, below the data rates afforded by DSL. Nevertheless,in competing for customers, the provider of a DOCSIS system often toutsthe peak data rates afforded by the DOCSIS system without focusing onthe fact that the channel is shared and the average data rate,therefore, decreases as more and more customers become active.

Note that a variety of DSL formats have and have proven effective incompeting with DOCSIS. Very-high-bit-rate DSL (VDSL) is a solution thatis particularly attractive due to the relatively high data rates enabledby VDSL as compared to other DSL solutions. Indeed, first generationVDSL provides data transmission up to about 52 Mega-bits per second(Mbps) downstream and about 16 Mbps upstream. Second generation VDSL,sometimes referred to as VDSL2, provides up to about 100 Mbpssimultaneously in the both the upstream and downstream directions.

Like several other DSL technologies, VDSL suffers from the effects ofcrosstalk. Current VDSL standards specify vectoring techniques thatallow crosstalk cancellation, and such techniques have been employed tocancel the crosstalk among subscriber lines in an effort to improve theperformance of VDSL signals and allow for longer reaches.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood with reference to the followingdrawings. The elements of the drawings are not necessarily to scalerelative to each other, emphasis instead being placed upon clearlyillustrating the principles of the disclosure. Furthermore, likereference numerals designate corresponding parts throughout the severalviews.

FIG. 1 is a block diagram illustrating a conventional communicationsystem.

FIG. 2 is a block diagram illustrating an exemplary embodiment of acommunication system in accordance with the present disclosure.

FIG. 3 is a block diagram illustrating an exemplary embodiment of afeeder distribution interface (FDI), such as is depicted by FIG. 2.

FIG. 4 is a block diagram illustrating an exemplary embodiment of anaccess multiplexer, such as is depicted by FIG. 3.

FIG. 5 is a block diagram illustrating an exemplary embodiment of aservice unit, such as is depicted by FIG. 4.

FIG. 6 is a block diagram illustrating an exemplary embodiment of aservice unit, such as is depicted by FIG. 5.

FIG. 7 is a block diagram illustrating an exemplary embodiment of acommunication system in accordance with the present disclosure.

FIG. 8 is a block diagram illustrating an exemplary embodiment of acommunication system in accordance with the present disclosure.

FIG. 9 is a block diagram illustrating an exemplary embodiment of afeeder distribution interface, such as is depicted by FIG. 8.

FIG. 10 is a block diagram illustrating an exemplary embodiment of aservice unit, such as is depicted by FIG. 9.

FIG. 11 is a block diagram illustrating an exemplary embodiment of acommunication system in accordance with the present disclosure.

FIG. 12 is a block diagram illustrating an exemplary embodiment of aservice unit, such as is depicted by FIG. 11.

FIG. 13 is a block diagram illustrating an exemplary embodiment of afeeder distribution interface, such as is depicted by FIG. 11.

FIG. 14 is a block diagram illustrating an exemplary embodiment of aservice unit, such as is depicted by FIG. 11.

FIG. 15 is a flowchart illustrating an exemplary method of controllingerror correction in a communication system, such as is depicted by FIG.11.

DETAILED DESCRIPTION

The present disclosure generally pertains to systems and methods forcommunicating among network distribution points. In one exemplaryembodiment, shared digital communication links, such as DSL links, areused to carry data between a first network point, such as a feederdistribution interface (FDI) or a central office (CO), and one or moredistribution points (DPs). Non-shared links may then carry the data fromany of the DPs. In one exemplary embodiment, the shared links are bondedto create a high-speed, shared data channel that permits peak data ratesmuch greater than what would be achievable without channel sharing. Forexample, if there is only one customer active during a particular timeperiod, then all of the capacity of the bonded channel is used toservice such customer permitting a relatively high peak data rate forthe customer. As more customers become active or, in other words,actively communicate via the bonded channel, the capacity of the channelis divided among the active customers. In such case, each customer'saverage data rate is below the peak data rate afforded by the system,but each active customer nevertheless benefits by the idleness of theother customers who are not actively communicating. Moreover, byenabling greater peak data rates, the system can be more competitivewith other communication systems, such as DOCSIS systems, which enablerelatively high peak data rates as described above.

To improve the quality of communication across DSL links and allow forlonger reaches, crosstalk vectoring is employed. In one exemplaryembodiment, a high bandwidth modulation format, such as VDSL, isemployed to communicate on both a network side and a customer premises(CP) side of a DP. Crosstalk vectoring is then used to cancel far-endcrosstalk (FEXT) as well as crosstalk, referred to herein as “crossovercrosstalk,” that couples from one side of the DP to the other.

In addition, at each DP, logic is configured to dynamically manage thedata rates occurring across the shared communication lines serviced bythe DP. When there is available capacity, the logic enables forwarderror correction (FEC) encoding and controls the parity level of the FECencoding (e.g., the number of parity bits per frame) based on the amountof available capacity.

FIG. 1 depicts a conventional system 20 for communicating data between aplurality of customer premises 22 and a network facility 25, such as acentral office. An optical fiber 31 extends from the network facility 25to a feeder distribution interface (FDI) 28. The optical fiber 31provides a high-speed channel that carries data for a plurality ofcustomer premises 22. Equipment at the FDI 28 demultiplexes data fromthe optical fiber 31 onto a plurality of connections 36, such astwisted-wire pairs, that extend to a distribution point (DP) 41. The FDIequipment multiplexes data in the reverse path from the communicationconnections 36 onto the optical fiber 31. In this conventional system20, there is generally a one-to-one correspondence between atwisted-wire pair running from the FDI 28 to the DP 41 and atwisted-wire pair running from the DP 41 to a customer premises 22, andthere is no bonding between the FDI 28 and the DP 41 in the system 20shown by FIG. 1. In some cases when multiple subscriber lines extend tothe same customer premises 22, the links extending from an intermediatepoint, such as the FDI 28, to such customer premises 22 may be bonded,but such bonded links are not shared by multiple subscribers.

As shown by FIG. 1, the DP 41 is coupled to at least one customerpremises 22 via at least one conductive connection 44, such as atwisted-wire pair. The physical connection 44 from the DP 41 to acustomer premises 22 is typically referred to as a “drop wire” or a“drop connection.” The length of a drop connection 44 is usually short,about 500 feet or less.

The portion of the system 20 from the network facility 25 to the FDI 28is referred to as the “feeder plant,” and the portion of the system 20from the FDI 28 to the DP 41 is referred to as the “distribution plant.”DSL (e.g., Asymmetric DSL (ADSL), Single-pair High-speed DSL (SHDSL), orVery-high-speed DSL (VDSL)) or other modulation techniques and protocolsmay be employed between the FDI 28 and the customer premises 22.

When DSL is employed between the FDI 28 and customer premises 22, theelement that multiplexes data from the DSL links onto a fiber link (anddemultiplexes the reverse path) is often referred to as a DSL AccessMultiplexer (DSLAM). The DSLAM often performs some level ofconcentration. In this regard, the data rate on the fiber optic linkoften is less than the sum of the data rates on all of the DSL links,and the DSLAM uses statistical multiplexing of data packets (eithervariable length frames or fixed length frames often referred to ascells) to combine (or separate, depending on the direction the data isbeing transmitted) the different data streams from (or to) theirrespective DSL links.

There are some natural preferred locations for the DSLAM due to thedesign of the existing copper infrastructure. In this regard, there areoften wiring terminals located at the junction between the feeder plantand the distribution plant (i.e., the FDI 28) and at the junctionbetween the distribution plant and the drop wire (i.e., the DP 41) thatprovide access to the individual pairs, allowing individual pairs fromone section to be connected to the other. These terminals also provide anatural location for the intermediate point DSLAM because of the ease ofaccessing the individual pairs to inject the DSL signal. When afiber-fed DSLAM is located at the FDI 28, the architecture is oftenreferred to as fiber-to-the-node (FTTN), and when the DSLAM is locatedat the DP 41, the architecture is often referred to as fiber-to-the-curb(FTTC). Note that the junction between the distribution and the dropgoes by several names around the world, and terms other than the“distribution point” may be used to describe such junction. Note alsothat the junction between the feeder plant and the distribution goes byseveral names around the world, and terms other than the “feederdistribution interface” may be used to describe such junction.

FTTC architectures offer more flexibility in the technology andmodulation format used in the digital transceiver because a drop cableoften only contains pairs destined for a single customer premises.Because spectrum compatibility with signals to other customer premisesis not required, it is often possible to use transceivers with lowercomplexity, cost, and power consumption than might be required in a FTTNarchitecture. In addition, the short length of the drop wire (typicallyabout 500 feet or less) allows for a high data rate, potentially inexcess of 100 Megabits per second (Mbps) in each direction. FTTCarchitectures have been deployed using ADSL links, VDSL links and10BASE-T Ethernet links in the past.

However, FTTC architectures require the installation of substantiallymore fiber routes than FTTN architectures. Thus, FTTN architectures havesubstantial cost saving benefits when working in a “brownfield”environment, where copper cable is already installed in the distributionplant

FIG. 2 depicts an exemplary embodiment of a communication system 50 thathas an FTTN architecture and provides relatively high peak data rates.Similar to the conventional system 20, the system 50 shown by FIG. 2 hasa feeder distribution interface (FDI) 52 that is coupled to an opticalfiber 54 extending from a network facility 55, such as a central office.The optical fiber 54 provides a high-speed channel that carries data fora plurality of customer premises 56. The FDI 52 demultiplexes data fromthe optical fiber 54 onto a plurality of conductive connections 63, suchas twisted-wire pairs, that extend to a plurality of distribution points(DPs) 66. The FDI 52 multiplexes data in the reverse path from thecommunication links 63 onto the optical fiber 54.

As shown by FIG. 2, each DP 66 is coupled to at least one customerpremises 56 via at least one conductive connection 69, such as atwisted-wire pair, referred to as a “drop connection.” The exemplaryembodiment shown by FIG. 2 depicts three customer premises 56 servicedby each DP 66, but any number of customer premises 56 may be serviced byany of the DPs 66 in other embodiments. In one exemplary embodiment,Ethernet protocol is used to communicate data across the connections 69,but other protocols may be used in other embodiments. Furthermore, forillustrative purposes, it will be assumed hereafter that DSLtransceivers are used for the communication across each of theconnections 63, but other types of transceivers may be used in otherembodiments.

As will be described in more detail below, the connections 63 extendingbetween the FDI 52 and a given DP 66 are bonded to provide a shared,high-speed data channel between the FDI 52 and such DP 66. This is incontrast to the conventional system 20 of FIG. 1 in which theconnections 36 between the FDI 28 and DP 41 are not bonded. As describedabove, the data for a given drop connection 44 of the system 20 iscarried by only one of the connections 36 between the FDI 28 and DP 41.

FIG. 3 shows an exemplary embodiment of the FDI 52. The FDI 52 comprisesan optical network unit (ONU) 77 that is coupled to an accessmultiplexer 79 via a conductive connection 81. The access multiplexer 79and the ONU 77 are shown separately, but the functionality of the ONU 77may be incorporated into the access multiplexer 79 such that a singledevice performs optical/electrical conversions, as well asmultiplexing/demultiplexing. Note that the access multiplexer 79 mayreside at various locations. As an example, the access multiplexer 79may be in close proximity to or in the same cabinet as a cross-connectpoint of the FDI 52 used for coupling the access multiplexer 79 to theconnections 63 and the ONU 77. In another exemplary embodiment, theaccess multiplexer 79 resides at a central office and interfaces to theloop plant through a distribution frame. Yet other locations of theaccess multiplexer 79 are possible.

The ONU 77 receives the optical data signal from the fiber 54 anddemodulates the optical data signal to recover the data carried by suchsignal. The ONU 77 then transmits a high-speed data stream to the accessmultiplexer 79 carrying the data destined for each of the customerpremises 56. Thus, the ONU 77 receives the optical data signaltransmitted across the fiber 54 and converts the received optical datasignal into an electrical signal carrying the data destined for thecustomer premises 56.

As shown by FIG. 3, the access multiplexer 79 is coupled to a serviceunit 88 at each respective DP 66 via a plurality of conductiveconnections 63. In one exemplary embodiment, the access multiplexer 79communicates DSL signals, such as VDSL signals, across the connections63 and may be referred to as a DSL access multiplexer or DSLAM. In otherembodiments, other types of signals may be communicated across theconnections 63.

In one exemplary embodiment, the access multiplexer 79 and the serviceunits 88 are configured to employ bonding techniques in order to bondthe connections 63 extending between such access multiplexer 79 andservice units 88 such that the connections 63 form a high-speed, bondeddata channel for each respective service unit 88. In this regard, asknown in the art, the bonding of communication connections generallyrefers to a process of fragmenting packets of a high-speed data streamfor transmission across such connections such that each fragment istransmitted across a respective one of the connections. The fragmentsare re-combined at the other end of the connections to recover thehigh-speed data stream. Thus, a plurality of bonded connections,collectively referred to as a “bonding group,” can be used to achieve anaggregate data rate that is higher than the data rate afforded by anyone of the connections. Exemplary bonding techniques are described incommonly-assigned U.S. Pat. No. 7,693,090, entitled “Systems and Methodsfor Discovery of PME Bonding Groups,” and filed on Nov. 14, 2006, whichis incorporated herein by reference. Exemplary bonding techniques arealso described in commonly-assigned U.S. patent Ser. No. 11/074,918,entitled “Network Access Device and Method for Protecting SubscriberLines,” and filed on Mar. 8, 2005, which is incorporated herein byreference.

Generally, during bonding, a packet is fragmented by logic, sometimesreferred to as a “bonding engine,” on one side of a communicationchannel comprising a plurality of links. For each fragment, a smallamount of overhead, such as a sequence indicator indicating thefragment's sequence among all of the packet's fragments, is appended tothe fragment. The fragments are transmitted through the channel, and anyfragment may travel across any link of the channel. A bonding engine onthe opposite side of the channel uses the sequence indicators toreassemble the fragments into the packet originally fragmented prior totransmission through the channel, and the packet ordering is maintained.

Note that the embodiment shown by FIG. 3 is exemplary. Any number of DPs66 can be serviced by the FDI 52, and the FDI 52 may include any numberof ONUs 77 and access multiplexers 79. Further, as described above, theaccess multiplexer 79 can be configured to perform optical/electricalconversions so that a separate ONU 77 is not necessary. In addition, anynumber of connections 63 can extend between the access multiplexer 79and any of the service units 88. The optical network that provides theoptical data signal can be a passive optical network (PON). However,other optical networks may be used to provide the optical signal inother embodiments.

It is also possible and likely for data to flow in the oppositedirection as that described above. In this regard, an access multiplexer79 may receive data from any customer premises 56 serviced by it. Forany such CP data received from the connections 63, the accessmultiplexer 79 multiplexes such data into a data stream for transmissionto the ONU 77, which converts the data stream into an optical datasignal for transmission across the optical fiber 54.

FIG. 4 depicts an exemplary embodiment of the access multiplexer 79. Theaccess multiplexer 79 has forwarding logic 89 that is coupled to theelectrical connection 81 carrying the high-speed data stream from theONU 77 (FIG. 3). The forwarding logic 89 is configured to selectivelyforward the data packets received from such high-speed data stream to aplurality of bonding engines 92 via conductive connections 93. In thisregard, the forwarding logic 89 is configured to forward the datapackets based on their destination addresses such that they ultimatelypass through the appropriate service unit 88 and are received at theappropriate customer premises 56.

Each bonding engine 92 is configured to divide into fragments itsrespective data stream received from the forwarding logic 89 fortransmission across the communication connections 63 to its respectiveservice unit 88. Specifically, each bonding engine 92 fragments receiveddata packets into a plurality of fragments and transmits each fragmentto a respective one of the transceivers 95 coupled to it. In some cases,such as for small data packets, a received packet might not befragmented and, thus, pass through the bonding engine 92 unchanged. Theexemplary embodiment of FIG. 4 shows three bonding engines 92, eachforming a respective bonding group 96-98. However, in other embodiments,other numbers of bonding engines and/or bonding groups are possible.

Each transceiver 95 has circuitry for terminating a respectiveconnection 63. Each transceiver 95 also modulates a carrier signal usingthe data fragments received from the bonding engine 92 coupled to it andtransmits the modulated signal across a respective connection 63 to aservice unit 88 at a DP 66. Thus, data from the optical data signalcarried by the fiber 54 (FIG. 3) is divided across the connections 63.In one exemplary embodiment, each transceiver 95 employs a DSL protocol(e.g., VDSL), but other types of protocols may be used in otherembodiments.

FIG. 5 depicts an exemplary embodiment of a service unit 88 coupled toone bonding group 96. The service units 88 for the other bonding groups97 and 98 may be configured similar to or identical to the service unit88 depicted by FIG. 5. As shown by FIG. 5, the service unit 88 has aplurality of transceivers 101 respectively coupled to the connections 63of the bonding group 96. Each transceiver 101 has termination circuitry,which includes active components, for terminating the connection 63coupled to it. Further, each transceiver 101 demodulates the signalreceived from its respective connection 63 to recover the data fragmentstransmitted across such connection 63. The data fragments aretransmitted to a bonding engine 105 that assembles the fragments andrecovers the high-speed data stream originally fragmented by the bondingengine 92 (FIG. 4) at the access multiplexer 79. The bonding engine 105transmits the recovered high-speed data stream to forwarding logic 111that is coupled to a plurality of transceivers 114.

As shown by FIG. 5, each transceiver 114 is coupled to a respective CPtransceiver 117 via at least one connection 69, and each transceiver 114has termination circuitry, which includes active components, forterminating the connection 69 coupled to it. The forwarding logic 111 isconfigured to forward the data packets of the high-speed data stream tothe transceivers 114 based on the destination addresses in the datapackets such that each data packet is ultimately received by the CPtransceiver 117 identified by the packet's destination address.

The exemplary embodiment depicted by FIG. 5 has three transceivers 114respectively coupled to three CP transceivers 117 at three differentcustomer premises 56. However, any number of transceivers 114,connections 69, CP transceivers 117, and customer premises 56 arepossible in other embodiments. For example, it is possible for more thanone connection 69 to be coupled between a transceiver 114 of the serviceunit 88 and a CP transceiver 117. Further, any customer premises 56 mayhave more than one CP transceiver 117.

By terminating the connections 63 and 69 at the DP 66, as describedabove, the wiring at the customer premises 117 is isolated from theconnections 63. Thus, any reflections caused by such CP wiring shouldnot affect the communication occurring over the bonded group 96, andsuch termination may allow more flexibility on modulation formats forthe bonded group 96. In addition, it is possible to employ signalprocessing techniques, such as crosstalk vectoring, to reduce crosstalkinterference affecting the signals transmitted across the connections63, as will be described in more detail hereafter.

When there is extended distance between the DPs 66, active transmissionfrom DP-to-DP can boost the rate of the bonded channel. FIG. 6 shows anexemplary embodiment of a communication system 200 having a plurality ofDPs 266 for servicing a plurality of customer premises 56, similar tothe embodiment depicted by FIG. 2. However, the DPs 266 are arranged foractive communication from DP-to-DP.

Each service unit 288 is coupled to at least one bonding group 96-98 andprovides the data from one of the bonding groups 96-98 to at least onecustomer premises 56. As an example, FIG. 7 shows the service unit 288for the DP 266 that is coupled directly to the FDI 52 and, thus, to eachof the bonding groups 96-98. As shown by FIG. 7, the bonding engine 105of the service unit 288 is configured to reassemble the fragmentscarried by the bonding group 96 and to recover the high-speed datastream originally fragmented at the FDI 52 (FIG. 6) and transmitted overthe bonding group 96. Further, the forwarding logic 111 forwards thedata packets of this high-speed data stream to the customer premises 56,as appropriate. Thus, the data carried by the bonding group 96 isprovided to the customer premises 56 in the same way as described abovefor FIG. 2.

The DP 266 shown by FIG. 7 has a plurality of transceivers 292, whichare each coupled to a respective connection 63 of the bonding groups 97and 98. Each transceiver 292 is configured to demodulate the data signalreceived from the FDI 52 in order to recover the digital data carried bysuch signal. The transceiver 252 then transmits the digital data toanother transceiver 299, which modulates a carrier signal with thedigital data to form a data signal, which is a regeneration of the datasignal received by the transceiver 292. This regenerated signal istransmitted downstream to the service unit 288 of the next DP 266. Thus,the service unit 288 shown by FIG. 7 serves as a repeater for thesignals carried by the bonding groups 97 and 98.

The next DP 266 that receives the regenerated signals downstream issimilarly configured to provide data from the bonding group 97 to aplurality of customer premises 56 and to regenerate the data signalscarried by the bonding group 98. Using DPs 266 as repeaters helps tokeep the length of the bonded channels short thereby helping to providehigher data rates through such channels. Note that it is not necessaryfor any DP 266 to provide a regenerated signal for the data signalspassing through it. For example, rather than demodulating a receiveddata signal and then using the data from the received signal to modulatea new carrier signal, a DP 266 may have amplifiers (not shown) thatamplify the received signal for transmission to the next DP 266.

In one exemplary embodiment, when there is active communication fromDP-to-DP, the data for multiple DPs share the same bonded channel in aneffort to provide even greater peak rates for at least some subscribers.FIG. 8 depicts an exemplary embodiment of a communication system 300 inwhich data for multiple DPs share the same bonded channel. Thecommunication system 300 has an FDI 352 and a plurality of DPs 366 forservicing a plurality of customer premises 56, similar to the embodimentdepicted by FIG. 2. However, the DPs 366 are arranged for activecommunication from DP-to-DP.

Further, a plurality of communication connections 373 forming a singlebonding group 375 extend from the FDI 352 to a DP 366, as shown by FIG.8. As will be described in more detail below, this bonding group 375carries data for each of the DPs 366.

FIG. 9 shows an exemplary embodiment of the FDI 352 shown by FIG. 8.Forwarding logic 375 of an access multiplexer 376 receives thehigh-speed data stream transmitted from the ONU 77 and forwards packetsof the high-speed data stream to a bonding engine 377. The bondingengine 377 is configured to fragment the data packets of this high-speedstream and distribute the fragments to a plurality of transceivers 382,which transmit the fragments across a plurality of communicationconnections 373, such as twisted-wire pairs. The embodiment of FIG. 7 issimilar to that shown by FIG. 4, which forms three bonding groups 96-98,except that a single bonding group 375 is used to carry the fragmentsfor multiple DPs 266. Note that the access multiplexer 376 may havetransceivers and/or other bonding engines not shown by FIG. 9 to whichthe forwarding logic 375 may forward data packets received from the ONU377.

FIG. 10 depicts an exemplary embodiment of the service unit 388 at theDP 366 that is coupled directly to the FDI 352. The service unit 388 hasa plurality of transceivers 391. Each of the transceivers 391 is coupledto a respective one of the connections 373 of the bonding group 375 anddemodulates the data signal received from such connection 373 to recoverthe fragments carried by the connection 373. A bonding engine 393reassembles the fragments and recovers the high-speed data streamoriginally fragmented by the bonding engine 377 (FIG. 9).

Forwarding logic 394 is configured to receive this high-speed datastream and to forward the data packets in this stream based on theirdestination addresses. In this regard, data packets destined for thecustomer premises 56 shown by FIG. 10 and coupled directly to theservice unit 388 by drop connections 69 are transmitted to transceivers114, as appropriate, such that they arrive at their respectivedestinations. The other data packets, which are destined for customerpremises 56 coupled directly to downstream DPs 366, are transmitted to abonding engine 396. The bonding engine 396 is configured to fragment thereceived data packets and distribute the fragments to a plurality oftransceivers 397, which transmit the fragments across a plurality ofcommunication connections 398, such as twisted-wire pairs. Thus, theconnections 398 form a bonding group 399 between the service unit 388shown by FIG. 10 and the service unit 388 of the next downstream DP 366.Note that this next downstream service unit 388 may be configuredsimilar to the one shown by FIG. 10 in order to provide a portion of thedata carried by the bonding group 399 to customer premises 56 coupleddirectly to the downstream service unit 388 and to provide the remainingportion of such data to another DP 366 via a bonding group 401 (FIG. 8).

Accordingly, in the embodiment depicted by FIG. 8, a given bondedchannel, such as a bonding group 375 or 399, may carry data for multipleDPs 366. Thus, the number of customers sharing the same bonded channelcan be increased making it more likely that, at any given time, agreater number of CP transceivers 117 serviced by the same bondedchannel will be inactive.

It should be noted that FIGS. 8-10 show the same number of communicationconnections within each bonding group 375, 399, and 401, but such afeature is unnecessary. For example, referring to FIG. 8, the bondinggroup 399 may have fewer connections 398 than the number of connections373 in the bonding group 375. Further, it is possible for the bondinggroup 399 to have more connections 398 than the number of connections373 in the bonding group 375. For example, a shorter distance or adifferent modulation format for the bonding group 375 relative to thebonding group 399 may allow the bonding group 375 to communicate moredata across the same number or fewer connections 373 as the number ofconnections 398 in the bonding group 399. Moreover, any bonding group375, 399, or 401 may have more or fewer connections than any of theother bonding groups.

FIG. 11 depicts an exemplary embodiment of a communication system 400having a plurality of DPs 422-424 for servicing a plurality of customerpremises 56 where there is active communication from DP-to-DP, similarto the embodiment depicted by FIG. 8. As described above for FIG. 8, anFDI 402 communicates across a plurality of connections 425 forming abonding group 429. Each connection 425 is coupled to a service unit 432of the DP 422. Except as is otherwise described herein, the FDI 402 isconfigured similarly to and operates the same as the FDI 352 of FIG. 8.

The service unit 432 is coupled to a service unit 433 at the DP 423 viaa plurality of connections 426 forming a bonding group 430. The serviceunit 433 is coupled to and communicates with equipment at one or morecustomer premises 56 via at least one drop connection 444. Further, theservice unit 433 is coupled to a service unit 434 at the DP 424 via aplurality of connections 427 forming a bonding group 431. The serviceunit 434 is coupled to and communicates with equipment at one or morecustomer premises 56 via at least one drop connection 455.

As described above for the embodiment shown by FIG. 8, each bondinggroup 429-431 may have the same number of connections as the otherbonding groups, or any bonding group may have a different number ofconnections relative to any other bonding group. In one exemplaryembodiment, there are N connections 425 of the bonding group 429 and Mconnections 426 of the bonding group 430, where N is larger than M.Further, the service unit 432 functions as a repeater. In a downstreamdirection, the service unit 432 receives data from the connections 425and transmits such data across the connections 426. Since there are nodrop connections for the DP 422, the aggregate data rate of the signalstransmitted across the connections 426 should match the aggregate datarate of the signals received from the connections 425. Similarly, in theupstream direction, the aggregate data rate of the signals transmittedacross the connections 425 should match the aggregate data rate of thesignals received from the connections 426.

The connections 425-427 that extend between DPs 422-424 and/or the FDI402 are collectively referred to as a “trunk” 463. In one exemplaryembodiment, the same modulation format is used for each leg of thetrunk. Unless otherwise specified herein, it will be assumed hereafterthat VDSL (e.g., first generation VDSL or VDSL2) is used for the signalscommunicated in both the upstream and downstream directions across theconnections 425-427. In other embodiments, other types of modulationformats may be used.

Since there is a greater number of connections 425 relative to theconnections 426, the data rate of each respective connection 425 may beless than the data rate of each respective connection 426 while theaggregate data rates are equal. Such is useful when, for example, the DP422 is located further from the FDI 402 than from the next downstream DP423. As known in the art, signals are attenuated as they propagateacross the connections 425-427. Using a lower data rate for eachrespective connection 425 allows a greater reach for the leg between theFDI 402 and the DP 422.

Further, in one exemplary embodiment, at least some data carried by theconnections 426 is transmitted to the customer premises 56 by dropconnections 444 thereby reducing the data requirements for the nextdownstream leg of the trunk 463. That is, since some of the datareceived from the connections 426 in the downstream direction istransmitted across the DP connections 444, less data needs to betransmitted across the connections 427 to the next downstream DP 424relative to data transmitted across the connections 426 feeding the DP423. Thus, in one exemplary embodiment, there are P connections 427,where P is less than M (i.e., the number of connections 426). Indeed, inone exemplary embodiment, P is equal to M−K, wherein K is the number ofdrop connections 444. However, other numbers of connections 427 arepossible in other embodiments, and it is possible for P to exceed Mand/or for M to exceed N.

As shown by FIG. 11, each service unit 432-434 has a respective controlelement 472-474 that is configured to control the service unit based ona respective set of configuration data 475-477. The control elements472-474 will be described in more detail hereafter.

Note that the signals communicated by the system 400 are susceptible tocrosstalk, which refers to energy that couples from one communicationconnection to another thereby interfering with the signals transmittedacross the connection that receives the crosstalk. Crosstalk generallydegrades the quality of signals communicated across connections that arepositioned within a close proximity of one another, such as within thesame binder, and the effects of crosstalk can be pronounced especiallyfor high bandwidth signals, such as VDSL signals.

There are various types of crosstalk that can affect signals propagatingalong a connection. Far-end crosstalk (FEXT) generally refers tocrosstalk that is received at one location but is induced by aninterfering signal transmitted at a remote location (e.g., the far endof a binder through which the signal is transmitted). Near-end crosstalk(NEXT) generally refers to crosstalk that is received at one locationand is induced by an interfering signal transmitted from the samelocation. As an example, when an interfering signal transmitted by theservice unit 432 in the downstream direction across a connection 426interferes with another signal transmitted by the service unit 432across another connection 426 in the downstream direction, the resultinginterference is referred to as FEXT. However, when an interfering signaltransmitted by the service unit 432 in the downstream direction across aconnection 426 interferes with a signal transmitted by the service unit433 in the upstream direction across a connection 426, the resultinginterference is referred to as NEXT, although NEXT does not generallyexist in a system in which upstream and downstream signals are frequencydivision multiplexed.

In one exemplary embodiment, the connections 425 are located in the samebinder (not shown), the connections 426 are located in another binder,and the connections 427 are located in yet another binder. Thus, thesignals propagating along the connections 425-427 are affected by FEXT.Even if the connections of a given bonding group are not located in thesame binder, the connections may be positioned close to one another ator within a service unit, such that the signals are neverthelessaffected by FEXT. In VDSL, upstream signals and downstream signals arefrequency division multiplexed. That is, the signals transmittedupstream are within one frequency range, and the signals transmitteddownstream are in another frequency range that does not overlap with thefrequency rage of the upstream signals. Thus, the signals communicatedacross the connections 425-427 should not be affected by NEXT.

The service units 432-434 and the FDI 402 are configured to performvectoring in order to cancel crosstalk from the signals communicatedacross the trunk 463 and drop connections 444 and 455. Vectoring is aknown technique by which signals are associated with coefficients,referred to as “vectoring coefficients,” that are used to estimatecrosstalk amounts, which can then be used to cancel crosstalk, as willbe described in more detail below.

In a discrete multi-tone (DMT) system, such as VDSL or ADSL, each signalcarries a plurality of tones in which each tone occupies a givenfrequency range that does not overlap with the frequency ranges of theother tones carried by the signal. In general, a given tone, referred toas “victim tone,” of one signal can be affected by crosstalk from tones,referred to as “interfering tones,” of other signals within the samefrequency range as the victim tone. In order to cancel crosstalk fromthe victim tone, a set of vectoring coefficients is defined in whicheach coefficient is associated with a respective one of the interferingtones. Vectoring logic, sometimes referred to as a “vector engine,” isconfigured to mathematically combine (e.g., multiply) the symbol of eachinterfering tone with its respective vectoring coefficient in order toestimate the amount of crosstalk induced by such symbol and affectingthe symbol of the victim tone. The vector engine then mathematicallycombines (e.g., subtracts) the crosstalk estimate from the symbol of thevictim tone in order to cancel the estimated crosstalk from the symbolof the victim tone. By performing such cancellation for each interferingtone affecting the victim tone, the vector engine effectively removescrosstalk from the symbol of the victim tone.

After such cancellation, the modified symbol of the victim tone isdecoded to determine an error signal indicative of the error in themodified symbol. Such error signal is provided to the vector engine,which adaptively updates the vectoring coefficients using the leastmeans square algorithm or some other known adaptive update algorithm sothat the coefficients can be adapted for changing line conditions. Suchvectoring techniques have conventionally been employed in order toremove FEXT from signals communicated in DSL systems. Similarly, theservice units 432-434 are configured to employ vectoring in order toremove FEXT from the signals communicated across the connections 425-427of the system 400.

However, in the system 400 depicted by FIG. 11, the signals are affectedby another type of crosstalk, referred to herein as “crossovercrosstalk” (COXT). COXT generally refers to crosstalk that couples fromone side of a service unit to another. As an example, in the context ofthe service unit 432, the connections 425 are not in the same binder asthe connections 426. However, the ends of the connections 425 may belocated close to the ends of the connections 426 at or inside of theservice unit 432 such that COXT couples from the connections 425 to theconnections 426 and vice versa. That is, a signal propagating along aconnection 425 may interfere with a signal propagating in the samedirection along a connection 426, and a signal propagating along aconnection 426 may interfere with a signal propagating in the samedirection along a connection 425.

Notably, COXT is dissimilar to FEXT that is cancelled by conventionalvectoring techniques. In particular, COXT is more similar to NEXT inthat COXT originates from signals transmitted by a service unit andaffects the signals received by this same service unit. That is, theinterfering tones are transmitted by a service unit, and the victimtones affected by such interfering tones are received by this sameservice unit. However, NEXT is typically associated with signals thatare transmitted within the same binder or a set of binders on the sameside of a service unit where the interfering tones travel in a differentdirection relative to the victim tone. COXT on the other hand isassociated with signals that are in different binders on different sidesof a service unit and that travel in the same direction. For example,COXT affecting a victim tone transmitted by the service unit 432 acrossa connection 426 in the downstream direction may be induced by aninterfering tone transmitted in the same downstream direction to theservice unit 432 across a connection 425 in a different binder. In suchan example, the interfering tones and the victim tone travel in the samedirection but in different binders.

In one exemplary embodiment, the service units 432 and 433 are bothconfigured to employ vectoring in order to cancel COXT. Exemplarytechniques for employing vectoring in order to cancel COXT are describedin commonly-assigned U.S. patent application Ser. No. 13/016,680,entitled “Systems and Methods for Cancelling Crosstalk in SatelliteAccess Devices” and filed on Jan. 28, 2011, which is incorporated hereinby reference.

FIG. 12 depicts an exemplary embodiment of the service unit 432 at theDP 422. The service unit 432 is similar to the embodiment depicted byFIG. 10 except that the service unit 432 is configured to performcrosstalk vectoring as will be described in more detail hereafter.

In this regard, the service unit 432 has a plurality of transceivers505-511 respectively coupled to the connections 425 of the bonding group429. For clarity purposes, each of the transceivers 505-511 shall bereferred herein as a “network-side transceiver.” Each network-sidetransceiver 505-511 is coupled to a bonding engine 515, which is coupledto forwarding logic 517. The forwarding logic 517 is coupled to abonding engine 522, which is coupled to a plurality of transceivers535-539. For clarity purposes, each transceiver 535-539 shall bereferred to as a “CP-side trunk transceiver.” Each CP-side trunktransceiver 535-539 is coupled to a respective connection 426 of thebonding group 430. For illustrative purposes, it will be assumedhereafter that each transceiver 505-511 and 535-539 employs VDSL, but itshould be emphasized that other modulation formats may be used in otherembodiments.

In the downstream direction, each transceiver 505-511 receives anddemodulates a respective VDSL signal to recover fragments, which arereassembled to by the bonding engine 515 to recover the data streamoriginally fragmented by a bonding engine of the FDI 402 (FIG. 11). Theforwarding logic 517 receives the data stream and forwards the packetsof the data stream to the bonding engine 522. The bonding engine 522fragments each packet into a plurality of fragments, and each fragmentis used by a respective transceiver 535-539 to modulate a carrier signalfor transmission across the respective connection 426 coupled to suchtransceiver.

As shown by FIG. 12, the service unit 432 has a control element 472 forcontrolling operation of the service unit 432 based on configurationdata 475 stored in memory 481. In the exemplary embodiment shown by FIG.12, the control element 472 is implemented in software, stored withinmemory of a processor 554, and executed by the processor 554. In otherembodiments, the control element 472 can be stored in and/or executed byother types of instruction execution devices. Further, the controlelement 472 can be implemented in hardware, software, firmware, or anycombination thereof. The exemplary processor 554 shown by FIG. 12 isconfigured to handle exception packets and control packets. In thisregard, when the forwarding logic 517 receives such a packet, theforwarding logic 517 traps the packet such that it is transmitted to theprocessor 554 rather than being forwarded to one of the bonding engines515 or 522. In this regard, in one exemplary embodiment, there is anembedded control channel provided by the trunk 463 so that the serviceunits 422-424 can communicate control packets to one another via theconnections 426 and 427. Other techniques for communicating controlinformation among the service units 422-424 are possible in otherembodiments.

As shown by FIG. 12, the service unit 432 also has vectoring logic 565for performing crosstalk vectoring in order to cancel crosstalk from thesignals communicated across the connections 425 and 426 based on sets ofvectoring coefficients 566, as will be described in more detail below.The vectoring logic 565 is coupled to each transceiver 505-511 and535-539 of the service unit 432 as shown by FIG. 12.

In one exemplary embodiment, the vectoring logic 565 uses sets ofvectoring coefficients 566 to cancel FEXT that couples from oneconnection 426 to another. In this regard, each tone communicated by orwith a respective one of the CP-side trunk transceivers 535-539corresponds to a set of coefficients 566, and the vectoring logic 565uses the corresponding coefficient set to cancel FEXT tone-by-toneinduced by other interfering tones communicated by or with the CP-sidetrunk transceivers 535-539. The set of coefficients 566 corresponding toa communicated tone includes coefficients respectively associated withthe interfering tones communicated across the connections 426.

As an example, assume that a set of coefficients 566 corresponds to anupstream tone, referred to hereafter as “victim tone” for this example,received by the CP-side trunk transceiver 535 from one of theconnections 426, which is referred to as the “victim connection” forthis example. The foregoing coefficient set includes coefficientsrespectively associated with the upstream tones, referred to as“upstream interfering tones,” communicated across the other connections426 that interfere with the victim tone.

In particular, for a given symbol of the victim tone, the vectoringlogic 565 receives such symbol from the CP-side trunk transceiver 535,and the vectoring logic 565 receives from the other CP-side trunktransceivers 536-539 the symbols of each of the upstream interferingtones communicated across the connections 426 at the same time as thereceived symbol of the victim tone. The vectoring logic 565 thencombines each upstream interfering tone with the coefficientrespectively associated with such interfering tone to determine anamount (“crosstalk contribution”) that the interfering tone affects thesymbol of the victim tone. The vectoring logic 565 then digitallycombines (e.g., subtracts) the determined crosstalk contribution withthe symbol of the victim tone to cancel the crosstalk induced by theinterfering tone. Such cancellation is performed tone-by-tone for eachupstream interfering tone such that the symbol of the victim tonefiltered by the vectoring logic 565 is substantially free of thecrosstalk induced by the upstream interfering tones.

After canceling crosstalk from the symbol of the victim tone, suchsymbol is transmitted back to the CP-side trunk transceiver 535, whichthen decodes the symbol and determines an error associated with thesymbol. The transceiver 535 transmits an error signal indicative of sucherror to the vectoring logic 565, which then adaptively updates the setof coefficients 566 corresponding to the victim tone via the least meanssquare (LMS) algorithm or some other known coefficient update algorithm.Similar techniques are used to cancel FEXT from each tone received by arespective one of the CP-side trunk transceivers 535-539. Accordingly,for each upstream symbol received by the CP-side trunk transceivers535-539, FEXT induced by the upstream signals propagating along theconnections 426 is canceled by the vectoring logic 565.

Similar vectoring techniques are used to cancel FEXT from downstreamtones transmitted by the CP-side trunk transceivers 535-539 across theconnections 426. In this regard, prior to transmission across theconnections 426, each CP-side trunk transceiver 535-539 transmits to thevectoring logic 565 the symbol of each downstream tone to be transmittedsimultaneously across the connections 426. The vectoring logic 565 thenprecodes the symbols such that FEXT that couples from one connection 426to another is canceled as the symbols propagate along the connections426.

In this regard, assume that the CP-side trunk transceiver 535 is totransmit a symbol of a downstream tone, referred to as the “‘victimtone” in this example, across the connection 426 coupled to it. For eachinterfering tone that will affect the symbol of the victim tone duringtransmission via the bonding group 430, the vectoring logic 565 receivesthe symbol of the interfering tone to be transmitted simultaneously withthe symbol of the victim tone across the connections 426 and combinessuch symbol with its associated vectoring coefficient to form a precodedvictim tone symbol which has compensated for the crosstalk induced bythe symbols of the interfering tones. The symbol of each victim tone issimilarly precoded for each interfering tone such that the symbolsreceived by the service unit 433 (FIG. 11) of the DP 423 substantiallyfree of FEXT. The service unit 433 decodes the symbol of the victim toneand generates an error signal indicative of the error in such symbol,and the service unit 433 transmits the error signal to the service unit432 allowing the vectoring logic 565 to update the set of coefficients566 corresponding to the victim tone. Accordingly, the vectoring logic565 is configured to cancel FEXT in both the upstream and downstreamsignals transmitted across the connections 426.

As shown by FIG. 13, the FDI 402 is configured similar to the FDI 352 ofFIG. 9 except that the FDI 402 has vectoring logic 503 that uses sets ofvectoring coefficients 504 to cancel FEXT from the signals carried bythe connections 425. In this regard, the FDI 402 has a plurality oftransceivers 511 that are respectively coupled to the connections 425,and the vectoring logic 503 is coupled to each of the transceivers 511.The vectoring logic 503 is configured to utilize the sets ofcoefficients 504 to cancel FEXT in the upstream and downstream signalscommunicated across the connections 425 in the same way that thevectoring logic 565 (FIG. 12) is described above as using the sets ofcoefficients 566 to cancel FEXT from the signals communicated across theconnections 426. In particular, the vectoring logic 503 receives thesymbols of the upstream signals and cancels FEXT from such symbols. Thevectoring logic 503 also precodes the symbols of the downstream signalsso that FEXT that couples from connection-to-connection is canceled asthe downstream signals propagate along the connections 425.

As shown by FIG. 12, the vectoring logic 565 is also coupled to andcommunicates with each of the network-side transceivers 505-511. Thevectoring logic 565 is configured to receive each symbol of each tonetransmitted by the network-side transceivers 505-511 across theconnections 425. Since these upstream tones are in the same frequencyrange as the upstream tones received by the CP-side trunk transceivers535-539 from the connections 426, COXT couples from the connections 425to the connections 426 and vice versa. The vectoring logic 565 isconfigured to use the upstream symbols transmitted by the network-sidetransceivers 505-511 to cancel the COXT that couples from theconnections 425 to the connections 426.

In this regard, consider the example described above in which thevectoring logic 565 is canceling FEXT from a victim tone received by theCP-side trunk transceiver 535 from the connection 426 coupled to it. Aset of vectoring coefficients 566 corresponding to the victim toneincludes coefficients associated with the upstream interfering tonestransmitted across the connections 425 by the network-side transceivers505-511. The vectoring logic 565 is configured to combine (e.g.,multiply) the respective symbol of each upstream interfering tonetransmitted across the connections 425 with its associated vectoringcoefficient to determine a respective crosstalk contribution that iscombined with (e.g., subtracted from) the symbol of the victim tone tocancel the COXT induced by the upstream interfering tone.

As an example, assume that an upstream tone (referred to in this exampleas the “upstream interfering tone”) transmitted by the network-sidetransceiver 505 across the connection 425 coupled to it. Also assumethat such upstream interfering tone is associated with a vectoringcoefficient (b) in a set of vectoring coefficients 566 corresponding tothe victim tone. In such example, the network-side transceiver 505transmits the symbol of the upstream interfering tone to the vectoringlogic 565. The vectoring logic 565 combines such symbol from thetransceiver 505 with coefficient b to determine a crosstalk contributionindicative of an estimated amount of COXT induced by the upstreaminterfering tone and affecting the symbol of the victim tone. Thevectoring logic 565 combines such crosstalk contribution with the symbolof the victim tone to cancel the COXT induced by the upstreaminterfering tone. Once each symbol of the interfering tones transmittedby the network side transceivers 505-511 (for canceling COXT) and theother trunk transceivers 536-539 (for canceling FEXT) has been combinedwith the symbol of the victim tone, the symbol of the victim tone istransmitted to the transceiver 535, which decodes the symbol andprovides an error signal as indicated above. The vectoring coefficientsused to estimate the crosstalk affecting the victim tone are thenadaptively updated based on the error signal.

Accordingly, for the victim tone received by the CP-side trunktransceiver 535, FEXT from upstream interfering tones carried by theconnections 426 and COXT from upstream interfering tones carried by theconnections 425 are both canceled thereby improving the quality of thevictim tone. In a similar manner, the vectoring logic 565 is configuredto cancel crosstalk in each upstream tone received by the CP-side trunktransceivers 535-539 from the connections 426.

Similarly, the vectoring logic 565 is configured to use the downstreamsymbols transmitted by the trunk transceivers 535-539 to cancel the COXTthat couples from the connections 426 to the connections 425. In thisregard, consider an example in which the network-side transceiver 505receives a downstream tone, referred to as “victim tone” in thisexample, affected by COXT that couples from downstream tones, referredto as “downstream interfering tones” in this example, transmitted acrossthe connections 426. A set of vectoring coefficients 566 correspondingto the victim tone includes coefficients associated with the downstreaminterfering tones transmitted across the connections 426 by the CP-sidetrunk transceivers 535-539. The vectoring logic 565 is configured tocombine (e.g., multiply) the respective symbol of each downstreaminterfering tone transmitted across the connections 426 with itsassociated vectoring coefficient to determine a respective crosstalkcontribution that is combined with (e.g., subtracted from) the symbol ofthe victim tone to cancel the COXT induced by the downstream interferingtone. Thus, the vectoring logic 565 is configured to cancel COXT thatcouples in both directions between the connections 425 and 426.

Referring again to FIG. 11, the service unit 433 at the DP 423 isconfigured to cancel FEXT and COXT according to techniques similar tothose described above for the service unit 432 of FIG. 12. FIG. 14depicts an exemplary embodiment of the service unit 433. As shown byFIG. 14, the service unit 433 comprises a plurality of network-sidetransceivers 605-609, bonding engines 615 and 622, forwarding logic 617,and a plurality of CP-side trunk transceivers 635-637. The service unit433 also comprises a plurality of transceivers 656 and 657, referred tohereafter as “drop transceivers,” that are respectively coupled to CPtransceivers 117 via drop connections 444. The service unit 433 furthercomprises a control element 473 that is configured to control operationof the service unit 433 based on configuration data 476 stored in memory659. In one embodiment, the control element 473 is implemented insoftware and stored in, as well as executed by, a processor 654, similarto the control element 472 of FIG. 12. However, in other embodiments,the control element 473 can be stored in and/or executed by other typesof devices, and the control element 473 can be implemented in hardware,software, firmware, or any combination thereof.

In the downstream direction, the bonding engine 615 reassemblesfragments from the connections 427 to recover the data stream originallyfragmented by the bonding engine 522 (FIG. 12) of the service unit 432,and the forwarding logic 617 forwards each packet. In the exemplaryembodiment shown by FIG. 14, a packet can be forwarded to a respectiveone of the drop transceivers 656 or 657 or to the bonding engine 622depending on the packet's destination. Each packet received by thebonding engine 622 is fragmented for transmission across the connections427.

In the upstream direction, the bonding engine 622 reassembles fragmentsfrom the connection 427 to recover the data stream originally fragmentedby the service unit 434 (FIG. 11). The forwarding logic 617 transmits adata stream, which includes packets from the bonding engine 622 andpackets from the drop transceivers 656 and 657, to the bonding engine615, and the bonding engine 615 fragments such packets for transmissionacross the connections 426.

The service unit 433 also comprises vectoring logic 665 that isconfigured to cancel crosstalk using sets of vectoring coefficients 667,similar to the vectoring logic 565 of FIG. 12. In particular, thevectoring logic 665 cancels FEXT affecting the signals communicatedacross the connections 427 using the same techniques described above forthe vectoring logic 565 to cancel FEXT affecting the signalscommunicated across the connections 426, including both FEXT thatcouples from one connection 427 to another and FEXT that couples fromthe drop connections 444 to the connections 427. The vectoring logic 665also cancels COXT that couples between the connections 426 and 427 usingthe same techniques described above for the vectoring logic 565 (FIG.12) to cancel COXT that couples between the connections 425 and 426.

The vectoring logic 665 further cancels FEXT affecting the signalscommunicated across the drop connections 444 using the same techniquesdescribed above for the vectoring logic 565 to cancel FEXT affecting thesignals communicated across the connections 426, including both FEXTthat couples from one drop connection 444 to another and FEXT thatcouples from the connections 427 to the drop connections 444. Asdescribed above, the vectoring logic 565 (FIG. 12) of the service unit432 cancels FEXT affecting the signals communicated across theconnections 426.

In addition, the vectoring logic 665 of the service unit 433 shown byFIG. 14 cancels COXT that couples between the drop connections 444 andthe trunk connections 426 using the same techniques described above forthe vectoring logic 565 (FIG. 12) to cancel COXT that couples betweenthe connections 425 and 426. In this regard, consider an example inwhich the network-side transceiver 605 receives a downstream tone,referred to as “victim tone” in this example, affected by COXT thatcouples from downstream tones, referred to as “downstream interferingtones” in this example, transmitted across the drop connections 444. Aset of vectoring coefficients 667 corresponding to the victim toneincludes coefficients associated with the downstream interfering tonestransmitted across the drop connections 444 by the drop transceivers 656and 657. The vectoring logic 665 is configured to combine (e.g.,multiply) the respective symbol of each downstream interfering tonetransmitted across the drop connections 444 with its associatedvectoring coefficient to determine a respective crosstalk contributionthat is combined with (e.g., subtracted from) the symbol of the victimtone to cancel the COXT induced by the downstream interfering tone.

Further, consider an example in which the drop transceiver 656 receivesan upstream tone, referred to as “victim tone” in this example, affectedby COXT that couples from upstream tones, referred to as “upstreaminterfering tones” in this example, transmitted across the trunkconnections 426. A set of vectoring coefficients 667 corresponding tothe victim tone includes coefficients associated with the upstreaminterfering tones transmitted across the trunk connections 426 by thenetwork-side transceivers 605-609. The vectoring logic 665 is configuredto combine (e.g., multiply) the respective symbol of each upstreaminterfering tone transmitted across the trunk connections 426 with itsassociated vectoring coefficient to determine a respective crosstalkcontribution that is combined with (e.g., subtracted from) the symbol ofthe victim tone to cancel the COXT induced by the upstream interferingtones. Thus, the vectoring logic 665 is configured to cancel COXT thatcouples in both directions between the connections 426 and 444.

Note that vectoring between any of the transceivers described above isgenerally simplified if each transceiver has the same modulation format.It is possible, however, for vectoring to occur between transceiversemploying different modulation formats, though the vectoringcalculations may be more complicated. For example, it is possible forthe drop transceivers 656 and 657 to employ VDSL while the CP-side trunktransceivers 635-637 employ VDSL2 and for vectoring to be performed tocancel crosstalk that couples from the trunk connections 427 to the dropconnections 444 and vice versa.

Also note that the service unit 434 (FIG. 11) is configured similar tothe service unit 433 of FIG. 14 except that the service unit 434 has notrunk transceivers or a bonding engine on a CP side of the service unit474, similar to the CP-side trunk transceivers 635-637 and bondingengine 627 of FIG. 14. In addition, it should be emphasized that variousdesign changes to the embodiment shown by FIGS. 11-14 are possible. Asan example, the number of components, such as connections andtransceivers shown by FIGS. 11-14, may be changed in any manner in orderto provide a desired capacity. Further, drop connections may beconnected to any DP, and there may be any number of DPs daisy-chainedtogether. Various other design changes would be apparent to a person ofordinary skill upon reading this disclosure.

As a mere example, it is possible to use point-to-multipoint connections(not shown) to communicate multicast flows to the DPs 422-424, asdescribed in commonly-assigned U.S. patent application Ser. No.12/839,402, entitled “Communication Systems and Methods for Using SharedChannels to Increase Peak Data Rates” and filed on Jul. 19, 2010, whichis incorporated herein by reference. In this regard, multicast flows maybe communicated via such point-to-multipoint connections while unicastflows are communicated via the point-to-point connections 425-427 shownby FIG. 11. However, it is possible for any unicast flow to becommunicated by the point-to-multipoint connections and for multicastflows to be communicated by the connections 425-427. In otherembodiments, yet other design changes are possible.

As described above, each service unit 432-434 respectively comprises acontrol element 472-474 and stores configuration data 475-477. Theconfiguration data 475-477 is indicative of the resources, capacities,and constraints of the service unit in which it is stored. As anexample, the configuration data within a given service unit may indicatethe number of ports in the service unit, a maximum data rate for eachport, and service level agreement (SLA) information specifyingperformance parameters, such as minimum data rate, maximum burst rate,etc. guaranteed to customers. The control elements 472-474 control theoperation of the service units 432-434, such as transmission bandwidth,in an attempt to ensure that there is sufficient capacity to accommodatethe traffic on the trunk 463 and to ensure that the specifiedperformance parameters are satisfied. As an example, the controlelements 472-474 may allocate bandwidth or control the data rates ofservice units 432-433 based on the configuration data 475-477. Thecontrol elements 472-474 may also establish priorities and otherparameters for handling congestion.

In one exemplary embodiment, the control elements 472-474 are configuredto control the data rates of the trunk transceivers to ensure that thereis sufficient capacity to handle the traffic carried by the trunk 463while ensuring that specified performance parameters are satisfied andto determine an amount of available capacity for each leg of the trunk463 that can be used for error correction. The control elements 472-474then selectively establish a level or type of error correction for eachleg of the trunk 463 based on the available capacity.

In this regard, each control element 472-474 is configured to determinea guaranteed aggregate service rate in each direction for each trunk legcoupled to its respective service unit 432-434. As an example, thecontrol element 472 based on the configuration data 475 or otherwisedetermines the guaranteed aggregate service rate for upstreamcommunication across the bonding group 429 and the guaranteed aggregateservice rate for downstream communication across the bonding group 430.Similarly, the control element 473 based on the configuration data 476or otherwise determines the guaranteed aggregate service rates forupstream communication across the bonding group 430, and the guaranteedaggregate service rate for downstream communication across the bondinggroup 431. Further, the control element 474 based on the configurationdata 477 or otherwise determines the guaranteed aggregate service ratefor upstream communication across the bonding group 431.

Note that the guaranteed aggregate service rate for a bonding group isthe minimum aggregate data rate that is guaranteed for the traffic ofservices propagating across the bonding group, and the guaranteedservice rate of a drop connection is the minimum data rate that isguaranteed for the traffic of services provided to the customer premisesacross such drop connection. Further, the guaranteed aggregate servicerate across a bonding group is generally a function of the guaranteedservice rates of the drop connections located downstream from thebonding group. Further, the guaranteed aggregate service rate across abonding group may also be a function of the physical capabilities of theservice unit as well as the specified performance parameters that shouldbe maintained by the service unit.

As an example, based on the physical configuration of the service unit433, including the number of connections 426, 427, and 444 coupled tothe service unit 433 and the types of transceivers employed within theservice unit 433, assume that in the downstream direction the serviceunit 433 is capable of (1) receiving up to 50 Mega-bits-per-second(Mbps) from the trunk connections 426, (2) transmitting up to 75 Mbpsacross the trunk connections 427, and (3) transmitting up to 100 Mbpsacross the drop connections 444. In such an example, the guaranteedaggregate service rate for the bonding group 431 in the downstreamdirection cannot be higher than 75 Mbps due to the fact that the totaldownstream capacity of the bonding group 431 is 75 Mbps. Further, theguaranteed aggregate service rate for the bonding group 431 in thedownstream direction cannot be higher than 50 Mbps due to the fact thatthe service unit 433 cannot receive more that 50 Mbps from the bondinggroup 430, which is the service unit's only downstream source in theexemplary embodiment depicted by FIG. 11.

In addition, for illustrative purposes, assume that the specifiedperformance parameters indicated by the configuration data 476 guaranteea total service rate of 10 Mbps in the downstream direction for all ofthe drop connections 444 and that the specified performance parametersindicated by the configuration data 477 guarantee a total service rateof 20 Mbps in the downstream direction for all of the drop connections455. That is, the sum of the guaranteed service rates for dropconnections 444 is 10 Mbps, and the sum of the guaranteed service ratesfor all drop connections 455 is 20 Mbps. In such an example, sinceservice unit 434 is the last service unit connected by the series ofbonding groups forming trunk 463, the guaranteed aggregate service ratefor the bonding group 431 in the downstream direction is the sum of theguaranteed service rates for all drop connections 455 or, in otherwords, 20 Mbps. For the service unit 433, the guaranteed aggregateservice rate is the sum of the guaranteed aggregate service rate of thebonding group 431 and the sum of the guaranteed service rates for all ofthe drop connections 444 in the downstream direction. Thus, assuming aguaranteed aggregate service rate of 20 Mbps for the bonding group 431,the guaranteed aggregate service rate for the bonding group 430downstream is 30 Mbps or, in other words, 20 Mbps+10 Mbps. For theservice unit 432, since there are no drop connections serviced by thisunit 432, the guaranteed aggregate service rate for the bonding group429 downstream is equal to the guaranteed aggregate service rate for thebonding group 430 downstream. In other examples, other techniques fordetermining the guaranteed aggregate service rate for any given trunkleg are possible.

In one exemplary embodiment, the control elements 472-474 are configuredto communicate with each other via a control channel or otherwise inorder to pass information indicative of the guaranteed aggregate servicerates for the trunk 463 and the guaranteed service rates of the dropconnections 444 and 455 so that each control element 472-474 can makecapacity and rate decisions based on the configurations and capacitiesof other distribution points. The control elements 472-474 then controlerror correction capabilities based on the service rate decisions.

As an example, using techniques described above, assume that the controlelement 472 determines that it is capable of delivering 50 Mbps acrossthe bonding group 430 to the service unit 433 and that all of theconnections 426 of the bonding group 430 are coupled between the serviceunits 432 and 433. In such case, the control element 472 could selectits guaranteed aggregate service rate for the bonding group in thedownstream direction to be 50 Mbps. However, further assume that thecontrol element 473, based on the configuration and capacity of theservice unit 433 as well as the performance requirements for the dropconnections 444 determines that the guaranteed aggregate service ratefor the bonding group 431 is 20 Mbps and that the sum of the guaranteedservice rates for all of the drop connections 444 coupled to the serviceunit 433 is 10 Mbps. In such an example, it is unnecessary for theservice unit 432 to guarantee a service rate of 50 Mbps since the nextservice unit 433 only guarantees a total of 30 Mbps for the next trunkleg defined by bonding group 431 and the drop connections 444. In theinstant example, the control element 472, based on control informationpertaining to the guaranteed service rates selected by the controlelement 473 for the service unit 33, preferably selects 30 Mbps as itsguaranteed aggregate service rate downstream across the bonding group430, thereby providing 20 Mbps of excess capacity that can be used forpurposes other than the communication of payload data.

For each leg of the trunk 463, the control elements 472-474 areconfigured to use excess capacity in order to transmit parityinformation, such as forward error correction (FEC) code words that canbe used to correct for transmission errors. For example, in theembodiment described above in which there is excess capacity of 20 Mbpsin the downstream direction for the leg between the service units 432and 433, the control element 472 is configured to control the serviceunit 432 such that parity information of up to 20 Mbps is appended tothe data packets transmitted from the service unit 472 to the serviceunit 473. In this regard, the control element 472 sets the parity levelfor the communication occurring across the bonding group 430 such that,when the service unit 432 is transmitting 30 Mbps across the bondinggroup 430, it should also be transmitting 20 Mbps of parity information.Using such parity information, the service unit 473 is able to correctfor at least some errors thereby enhancing the quality of the downstreamchannel defined by the bonding group 430. In general, the greater thatthe excess capacity is for any given leg, the more parity informationthat can be inserted into the data channel thereby increasing thequality of the data channel. Since error correction is enabled only tothe extent that excess capacity allows, the use of parity informationfor at least some legs should not adversely affect the effective datarate of the trunk 463.

An exemplary use and operation of the system 400 in controlling errorcorrection in the downstream direction will now be described below withparticular reference to FIG. 15. Similar techniques may be used by thecontrol elements 472-474 to control error correction in the upstreamdirection.

Initially, the control element 474 determines, based on theconfiguration data 477, the guaranteed service rate for each dropconnection 455 in the downstream direction while ensuring that thedetermined guaranteed service rate for each respective drop connection455 is equal to or less than the downstream capacity for such dropconnection 455. The control element 474 sums the guaranteed servicerates for all of the drop connections 455 coupled to the service unit434 and transmits such sum via a control channel of the bonding group431 to the service unit 433.

The control element 473 is configured to determine the guaranteedaggregate service rate for the bonding group 431 in the downstreamdirection based on the control information received from the serviceunit 434, as shown by block 752 of FIG. 15. In this regard, the controlelement 473 determines the downstream capacity of the bonding group 431based on the configuration data 476 or otherwise, and selects theguaranteed aggregate service rate for the bonding group 431 to be theminimum of the total downstream capacity of the bonding group 431 andthe sum of the guaranteed service rates of the drop connections 455, asindicated by the control information transmitted to the service unit 433from the service unit 434.

After determining the guaranteed aggregate service rate for the bondinggroup 431, the control element 473 calculates the excess capacity forthe bonding group 431 in the downstream direction, as shown by block 754of FIG. 15. Such excess capacity is equal to the difference between thetotal downstream capacity for the bonding group 431, as indicated by theconfiguration data 476 or otherwise, and the guaranteed aggregateservice rate selected by the control element 473 for the bonding group431 in the downstream direction.

The control element 473 also determines, based on the configuration data476, the guaranteed service rate for each drop connection 444 in thedownstream direction while ensuring that the determined guaranteedservice rate for each respective drop connection 444 is equal to or lessthan the downstream capacity for such drop connection 444. The controlelement 473 sums the guaranteed service rates for all of the dropconnections 444 coupled to the service unit 433 and transmits such sumvia a control channel of the bonding group 430 to the service unit 432,as shown by blocks 755 and 763 of FIG. 15, thereby enabling the controlelement 472 to consider such guaranteed service rates when selecting theguaranteed aggregate service rate in the downstream direction for thebonding group 430.

The control element 473 also establishes error correction for thebonding group 431 based on the excess capacity calculated in block 754.In one exemplary embodiment, the control element 473 uses all of theexcess capacity for communicating parity information. Thus, the controlelement 473 controls the format of the packets transmitted downstreamacross the bonding group 431 such that data rate for transmitting theparity information is equal to the data rate corresponding to the excesscapacity calculated in block 754. If desired, less amount of parityinformation may be communicated, thereby preserving at least some of theexcess capacity for other purposes.

The control element 472 of the service unit 432 is configured to utilizesimilar techniques to determine the guaranteed aggregate service ratefor the bonding group 430 in the downstream direction. Note that thereare no drop connections coupled directly to the service unit 432. Thus,there are no service rates to sum in block 755 of FIG. 15.

It should be emphasized that the embodiments described herein areexemplary. As an example, bonding is described as providing sharedchannels for the trunk 263. However, other techniques, such asmultiple-input and multiple-output (MIMO) communication techniques, maybe used to provide shared channels for the trunk 463. Also, having anoptical fiber 54 (FIG. 2) is unnecessary. As an example, the DP 422 maybe coupled to a central office without the use of fiber. Various otherdesign changes and modifications would be apparent to one of ordinaryskill upon reading this disclosure.

Now, therefore, the following is claimed:
 1. A communication system,comprising: a first distribution point positioned along a trunkextending from a network facility, the first distribution point having afirst service unit coupled to a first plurality of communicationconnections of the trunk and configured to receive from the firstplurality of communication connections a plurality of data flowsdestined for customer premises (CP) transceivers at a plurality ofcustomer premises, each of the first plurality of communicationconnections shared by each of at least a first plurality of the CPtransceivers; and a second distribution point positioned along the trunkand having a second service unit coupled to the first service unit via asecond plurality of communication connections of the trunk, each of thesecond plurality of communication connections shared by each of at leasta second plurality of the CP transceivers, wherein the first serviceunit is configured to employ crosstalk vectoring to cancel crosstalkaffecting signals communicated across the first plurality ofcommunication connections, and wherein the first service unit isconfigured to employ crosstalk vectoring to cancel crosstalk affectingsignals communicated across the second plurality of communicationconnections.
 2. The system of claim 1, wherein the first service unit isconfigured to employ crosstalk vectoring to cancel crossover crosstalkthat couples between the first plurality of communication connectionsand the second plurality of communication connections.
 3. The system ofclaim 1, wherein one of the first plurality of CP transceivers iscoupled to the first service unit via a drop connection extending fromthe first service unit to the one of the first plurality of CPtransceivers.
 4. The system of claim 3, wherein the first service unitis configured to employ crosstalk vectoring to cancel crosstalk thatcouples between the drop connection and at least one of the first andsecond plurality of communication connections.
 5. The system of claim 1,further comprising a third distribution point positioned along the trunkand having a third service unit coupled to the second service unit via athird plurality of communication connections, wherein the second serviceunit is configured to employ crosstalk vectoring to cancel crossovercrosstalk that couples between the second plurality of connections andthe third plurality of connections.
 6. The system of claim 5, wherein atotal number of communication connections connecting the first serviceunit to the second service unit is greater than a total number ofcommunication connections connecting the second service unit to thethird service unit.
 7. The system of claim 1, wherein the first serviceunit is configured to bond the first plurality of communicationconnections, thereby forming a first bonding group, and to bond thesecond plurality of communication connections, thereby forming a secondbonding group.
 8. The system of claim 1, wherein the first service unithas a control element configured to receive from the second service unitcontrol information indicative of guaranteed service rates for thesecond service unit, and wherein the control element is configured tocontrol error correction for signals communicated across the secondplurality of communication connections based on the control information.9. The system of claim 8, wherein the control element is configured toselect, based on the control information, a guaranteed aggregate servicerate for the second plurality of communication connections.
 10. Thesystem of claim 9, wherein the control element is configured todetermine a difference between the guaranteed aggregate data rate forthe second plurality of communication connections and a total capacityof the second plurality of communication connections, and wherein thecontrol element is configured to control the error correction based onthe difference.
 11. The system of claim 1, wherein the first serviceunit is configured to use a modulation format for communication acrossthe first plurality of communication connection, and wherein the secondservice unit is configured to use the modulation format forcommunication across the second plurality of communication connections.12. The system of claim 11, wherein the modulation format isvery-high-bit-rate digital subscriber line (VDSL).
 13. A method,comprising: receiving, at a first service unit of a first distributionpoint of a network, a plurality of data flows from a first plurality ofcommunication connections of a network trunk coupled to the firstservice unit, wherein the data flows are destined for customer premises(CP) transceivers at a plurality of customer premises, and wherein eachof the first plurality of communication connections is shared by each ofat least a first plurality of the CP transceivers; transmitting at leastone of the data flows from the first service unit to a second serviceunit at a second distribution point of the network via a secondplurality of communication connections of the network trunk, whereineach of the second plurality of communication connections is shared byeach of at least a second plurality of the CP transceivers; performingcrosstalk vectoring to cancel crosstalk affecting signals communicatedacross the first plurality of communication connections; and performingcrosstalk vectoring to cancel crosstalk affecting signals communicatedacross the second plurality of communication connections.
 14. The methodof claim 13, further comprising performing crosstalk vectoring to cancelcrossover crosstalk that couples between the first plurality ofcommunication connections and the second plurality of communicationconnections.
 15. The method of claim 13, wherein one of the firstplurality of CP transceivers is coupled to the first service unit via adrop connection extending from the first service unit to the one of thefirst plurality of CP transceivers.
 16. The method of claim 15, furthercomprising performing crosstalk vectoring to cancel crosstalk thatcouples between the drop connection and at least one of the first andsecond plurality of communication connections.
 17. The method of claim13, further comprising: transmitting at least one of the data flows fromthe second service unit to a third service unit at a third distributionpoint of the network via a third plurality of communication connectionsof the network trunk; and performing crosstalk vectoring to cancelcrossover crosstalk that couples between the second plurality ofcommunication connection and the third plurality of communicationconnections.
 18. The method of claim 17, wherein a total number ofcommunication connections connecting the first service unit to thesecond service unit is greater than a total number of communicationconnections connecting the second service unit to the third serviceunit.
 19. The method of claim 13, further comprising: bonding the firstplurality of communication connections, thereby forming a first bondinggroup; and bonding the second plurality of communication connections,thereby forming a second bonding group.
 20. The method of claim 13,further comprising: transmitting at least one of the data flows from thesecond service unit to a third service unit at a third distributionpoint of the network via a third plurality of communication connectionsof the network trunk; determining a guaranteed aggregate service ratefor the third plurality of communication connections; determining aguaranteed service rate for at least one drop connection coupled to thesecond service unit; transmitting control information from the secondservice unit to the first service unit, the control information based onthe guaranteed aggregate service rate and the at least one guaranteedservice rate; and determining a guaranteed aggregate service rate forthe second plurality of communication connections based on the controlinformation.